1. Field of the Invention
The present invention relates to an improved process for reducing the amount of molecular oxygen present in an inert processing atmosphere. In many known processes, such as the preparation or processing of pure metals, metal alloys, ceramics and/or semiconductors, it is conventional to conduct the process in an inert atmosphere in order to shield the reaction and/or materials against unwanted oxidation. While this is effective for most processes, it is not satisfactory in cases where even the formation of minor amounts of oxide impurities cannot be tolerated, which oxide impurities can result from the presence of small or trace amounts of oxygen which can be absorbed or adsorbed in the system or in the materials being processed.
2. Discussion of the Prior Art
It is conventional to form and sinter some metals, metal alloys, ceramics and/or semiconductors in an inert reducing atmosphere in order to prevent unwanted oxidation reactions, and reference is made to U.S. Pat. Nos. 3,196,007 and 4,088,475. It is also known to incorporate scavenger compounds which absorb or react with any oxygen present in the system, or to include compounds which develop reducing gases for reaction with any oxygen present in the system, and reference is made to U.S. Pat. Nos. 3,992,200 and 3,050,386.
The prior art evidences the fact that even an inert reducing atmosphere does not provide absolute protection against the presence of molecular oxygen. When a reducing gas such as hydrogen is present in the protective inert gas, the reaction atmosphere will contain H.sub.2, water vapor and, if equilibrium is attained, an oxygen potential corresponding to the H.sub.2 /H.sub.2 O ratio at the existing temperature and pressure. Unfortunately such atmospheres are not completely effective for preventing oxidation. Firstly, there is always at least a small amount of oxygen gas present in an inert gas system, which oxygen potential can be diminished but not eliminated by incorporating hydrogen gas, provided that system and the reactants will not suffer from the presence of hydrogen and/or water vapor. Secondly, the reaction between hydrogen and oxygen does not always proceed to equilibrium, and may result in an oxygen potential which is much higher than if equilibrium is obtained.